Does 7D really have custom shutter speeds ?

[Jester2138]

Are you saying that, visually, there are only 4 fps if you set the shutter at 1/4 (which is what I'm saying), but in the digital signal of 1's and 0's, its recorded as 24 fps? Basically that you have duplicated frames?

[Martti Ekstrand]

Originally Posted by Jester2138

Erm... I'll say it again... It's physically impossibly to expose a frame for longer than 1/24 if your at 24p (it's like saying your playing half-notes on an instrument that's only capable of eighth notes...). If your camera says "1/2" then it's not actually shooting 24p...

As I say in both the thread about "A Kindling Light" and in the comments at Vimeo I shot with the GH1 set to a 1/2 sec shutter and ended up with a file that had 2 frames for every real-time second recorded. Just like undercranking a film camera to 2 fps. I didn't want to derail this thread about 7Ds abilities so please ask any further in the thread about my clip.

Originally Posted by zephyrize

it's like f-numbers, there are f2, f2.8, f3.2, but no such thing as f2.1 or f3.0 ...

Umm... there is actually but still camera lenses mostly have click stops at fixed values. Cine lenses on the other hand have stepless aperture rings to both being able to fine-tune exposure and handle camera moving between dark and bright places. Duclos Lenses sell the Zeiss ZF series cine-modded with gear rings and the aperture mechanism de-clicked.

http://www.ducloslenses.com/DL/ZeissZF.html

[TimurCivan]

probbaly got it done by putting the cam in still mode , and rattling off shots @ 1/2 sec shutter @ 2 FPS, then dropping them into the timeline.

As far as available shutter speeds go, its according to 150 year old laws of Fstops, and exposure by shutter duration.

That isnt going to change. actually, there should only be B, 2sec, 1 sec, 1/2, 1/4, 1/8, 1/16th, 1/30, 1/60, 1/125, 1/250, 1/500, anything higher is the land of newer cameras, cameras from the 50's 60's 70's, usually quit around 1/1000th of a second. IN digital, the 1/8000th avialable. thats CRAZY fast. CRAZY. like "stop droplets of water in mid air, maybe even see a bullet" fast.

you make up the exposure differences between the "coarse" shutter speed stops, with the 1/2 stop and 1/3 stops on the apeture. Remeber in the old days on Film, being a half stop under or over exposed.... not really a big deal. In video.. it kinda is, you really gotta nail your exposures.

[Martti Ekstrand]

Originally Posted by TimurCivan

probbaly got it done by putting the cam in still mode , and rattling off shots @ 1/2 sec shutter @ 2 FPS, then dropping them into the timeline.

No, I shot it in creative movie mode with shutter speed at 1/2 getting a AVCHD file.

[TimurCivan]

oh wow didint know the GH1 did that.... cool

[Chris_TC]

Originally Posted by Blackout

This is not true. The frame rate of 24p is the rate of the capture of the image, not the shutter, so you have 24p (all films) capturing at 24 frames per second all sorts of different shutter speeds, from very fast to much much slower than the 24p rate. You could have a shutter wide open getting big blurs, written to 24 frames per second.

LOL, is this really so hard to understand? I thought Jester had explained it fairly well.

If you need 24 pictures per second, no picture can be exposed longer than 1/24th of a second. So if a video camera allows you to set the shutter speed to 1/12th of a second, you will end up with 12 different frames, not with 24. In a 24fps timeline, every other frame is doubled.

[ydgmdlu]

Exactly. How can a camera possibly capture 24 frames per second while allowing 1/12th second exposure per frame? 24 frames times 1/12th second exposure is 24/12=2 seconds. So two seconds of total exposure time is somehow being fit into one second of video? The camera has to reset the sensor before rescanning for the next frame. And even if it didn't have to do that, the results wouldn't be pretty...

Let's say that there's a hypothetical camera that actually does shoot 24 different frames per second, without any frame duplication, while allowing literally any shutter speed, no matter how slow. Let's say that you set an exposure time of one second. The long exposure time doesn't just affect image blur. The brightness of the image itself changes with time. At the 1/24th second mark, the image would be very dark, while at the one-second mark, the image would be very bright. The brightness would change noticeably with every frame, such that one second of footage will show the scene rapidly getting brighter and brighter. Remember, the longer the exposure, the more light is being collected.

Having the shutter "wide open" is known as a 360-degree shutter. A 360-degree shutter matches the frame rate (i.e. 1/24 for 24 fps, 1/30 for 30 fps, etc.).

[Barry_Green]

Originally Posted by Jester2138

Are you saying that, visually, there are only 4 fps if you set the shutter at 1/4 (which is what I'm saying), but in the digital signal of 1's and 0's, its recorded as 24 fps? Basically that you have duplicated frames?

Yes, duplicated frames. The amount of duplication depends on how slow the shutter is set to.

Look at it this way -- the recording system has no choice but to record 24 frames per second. But the imaging system cannot feed the recording system any faster than the exposure rate. So, the imaging system finishes with a frame and sends it to the recorder, and then starts exposing the next frame. It will hold that frame for as long as the shutter's duration. 1/24 of a second later, the recorder will ask for another frame. If the imaging system isn't done exposing the current frame, the recorder will just duplicate the last frame it got. And on and on.

So if you shoot at 1/2 second exposure, the maximum number of distinct frames per second that the imager can create, is two. That's all that's possible. It will hold that frame for an entire half of a second, and therefore it can only image two frames per second, with each taking 1/2 second to expose.

The recording system, however, will still record 24fps. So if it has to record the first frame 12 times, and then the second frame 12 times, that's what it will do.

The slower the shutter speed, the more duplicated frames. At any speed 1/24 or faster, there will be no duplication. But as soon as you go slower than 1/24, you get into frame duplication -- 1/12 = 12 fps (or one duplicate for every individual frame); 1/8 = 8 fps (or two duplicated frames for every individual frame), etc.

Same thing happens with 60p, if you set the shutter to 1/50 you will get duplicate frames. Any speed from 1/30 to 1/50 results in an effective unique frame rate of 30fps, any speed from 1/20 to 1/29.999 = an effective frame rate of 20fps, any speed from 1/15 to 1/19.9999 = an effective frame rate of 15fps, etc.

[Jester2138]

Thanks Barry. I was trying to explain the same thing to Blackout.

[VillageBoi]

Hi guys, newbie here. I hear all you're saying, however, back to the original issue which my one day old 7D has. In 720 mode 'PAL' I cannot get my shutter to 1/50 which I want to do and many others do. All it does is 1/60, 1/80/ 1/100 and others but no 1/50 - it's driving me nuts!!

I called Canon and they said theyll email back - who knows when lol. Has anyone been able to find a solution? In 720 mode I also have strobbing effect no matter what shutter speed - it's all good in 1080 though.